Let 5 digit numbers be constructed using the digits 0, 2, 3, 4, 7, 9 with repetition allowed, and arranged in ascending order with serial numbers. Then the serial number of the number 42923 is \_\_\_\_\_\_\_.
Answer: 2997
Solutions · 1
Official solution
Working through the position of 42923 digit by digit among all valid 5-digit numbers (first digit nonzero, from {2,3,4,7,9}, remaining digits from all 6 available digits), the cumulative count up to and including 42923 works out to:
\[\text{Serial number} = 2997\]